Conventionally, the keys of a keyboard device are arranged in a keyboard matrix. Since the number of conductor lines used in the keyboard matrix is not very large, the fabricating cost of the keyboard device is reduced and the assembling complexity is simplified. However, the conventional keyboard device usually has a ghosting problem.
FIGS. 1A˜1D schematically illustrate some situations of generating the ghosting problem in a keyboard matrix. As shown in the drawings, two column signal lines C(1), C(2) and two row signal lines R(1), R(2) of the keyboard matrix extending across each other two define four key units KU(1,1), KU(1,2), KU(2,1) and KU(2,2). The key unit KU(1,1) is connected with the first column signal line C(1) and the first row signal line R(1). The key unit KU(1,2) is connected with the first column signal line C(1) and the second row signal line R(2). The key unit KU(2,1) is connected with the second column signal line C(2) and the first row signal line R(1). The key unit KU(2,2) is connected with the second column signal line C(2) and the second row signal line R(2). In the drawings, the solid dots indicate the depressed key units, and the open dot indicates the non-depressed key. When one of the key units is depressed, the column signal line and the row signal line connected with the depressed key unit are electrically conducted. For example, if the key unit KU(1,1) is depressed, the first column signal line C(1) and the first row signal line R(1) are electrically conducted.
A keyboard controller (not shown) will sequentially scan the column signal lines and detect the voltage levels of all row signal lines. In case that the keyboard controller issues a scan signal to the first column signal line C(1) and the key unit KU(1,1) is depressed, the keyboard controller determines that the key unit KU(1,1) is depressed according to the high level state of the first row signal line R(1).
In the situation of FIG. 1A, the key unit KU(1,1) is not depressed, but the other key units KU(1,2), KU(2,1) and KU(2,2) are depressed. When the keyboard controller issues a scan signal to the first column signal line C(1), the first row signal line R(1) is in the high level state through the key units KU(1,2), KU(2,1) and KU(2,2). Under this circumstance, the keyboard controller erroneously determines that the key unit KU(1,1) is depressed according to the high level state of the first row signal line R(1).
In the situation of FIG. 1A, the key unit KU(1,1) is erroneously determined as a depressed key. In the situation of FIG. 1B, the key unit KU(1,2) is erroneously determined as a depressed key. In the situation of FIG. 1C, the key unit KU(2,1) is erroneously determined as a depressed key. In the situation of FIG. 1D, the key unit KU(2,2) is erroneously determined as a depressed key. The erroneously-determined keys are called ghost keys.
As mentioned above, the keyboard controller may erroneously determines that a specified key unit is depressed when the specified key unit is not depressed but the neighboring key units are depressed. Under this circumstance, the ghosting problem occurs.
Therefore, there is a need of providing a keyboard device with an anti-ghosting function.